Having precise geometric information for components of an imaging system, such as the positional coordinates and orientation of the X-ray detector and locations of the X-ray tube and X-ray detector, is a basic requirement for obtaining accurate data content, particularly affecting the image quality of reconstructed images. Mismapping between the intended object space and projection images can degrade spatial resolution and can lead to various types of image artifacts, such as ring artifacts.
The spatial geometry of the imaging system can be well-defined when using stationary imaging scanners and scanning apparatus that fix the position of the X-ray source and detector, such as using a C-arm or other mounting mechanism. Where this geometry is fixed by the imaging system, geometric calibration is straightforward and can be performed at periodic intervals using a calibration phantom.
However, with the introduction of portable and mobile digital X-ray imaging apparatus, the problem of geometric calibration becomes more acute. When used with bedridden patients, for example, it can be necessary to manually position the detector behind the patient and to determine the relative position of the X-ray source to the detector. Accurate calculation of the geometry of the imaging components is needed in order to obtain the best possible image quality under these challenging conditions, both for conventional 2-D radiography and for 3-D image reconstruction imaging, such as for tomosynthesis, computed tomography (CT), and cone-beam computed tomography (CBCT) imaging. With manual positioning of the source and detector components and the need for correlating the position of these devices to each other, each imaging exam requires separate geometric calibration.
It should be noted that calibration apparatus and methods should not compromise image quality, the mechanical integrity and usability of the detector, or protective features that eliminate or significantly reduce the likelihood of stray radiation.
It can thus be appreciated that there is a need for automated calibration apparatus and methods to support portable radiographic imaging apparatus.
The background above is provided for general overview information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The invention is defined by the claims.